The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Since 1990s, multicarrier technology has become a hot technology of broadband wireless communications. The basic concept of the multicarrier technology lies in that a broadband carrier is divided into a plurality of subcarriers and data is transmitted simultaneously on the divided subcarriers. In most of applications, the width of the subcarrier is less than a coherence bandwidth of a channel. Thus, on a frequency selective channel, the fading on each subcarrier is a flat fading, so that the crosstalk between user data symbols is reduced, and no complex channel equalization is needed. Therefore, it is suitable for the high-rate transmission of data. The existing multicarrier technology has various forms, such as Orthogonal Frequency Division Multiplex Access (OFDMA), Multiplex Carrier CDMA (MC-CDMA), Multiplex Carrier-Direct Spread-CDMA (MC-DS-CDMA) and Time Frequency (TF) domain two-dimensional expansion. Additionally, various expanded technologies based on the technologies are also included.
The Orthogonal Frequency Division Multiplex (OFDM) technology is a representative technology in the multicarrier technologies. In the OFDM technology, a given channel is divided into several orthogonal subchannels in a frequency domain, and it is allowed that spectrums of the subcarriers overlap partially, because different data signals may be separated from the overlapped subcarriers when the different subcarriers are orthogonal to each other.
FIG. 1 is a schematic diagram showing a modulation and demodulation process of a basic OFDM system in the prior art. As shown in FIG. 1, in the OFDM system, a channel coding and interleaving process is first performed on the user data, and the data after the coding and interleaving process is modulated to form a user data symbol through a modulation mode (such as, Binary Phase Shift Keying, BPSK, Quadrature Phase-Shift Keying, QPSK, and Quadrature Amplitude Modulation, QAM), and the user data symbol is modulated to a radio frequency by an OFDM operation. The demodulation process is opposite to this process, and a repeat description thereof is omitted.
In the OFDM operation, firstly, a serial/parallel conversion is performed on the user data symbol to form a plurality of low-rate sub-data streams, and each sub-data stream occupies a subcarrier. The process for mapping each sub-data stream into a corresponding subcarrier may be implemented via an Inverse Discrete Fourier Transformation (IDFT) or Inverse Fast Fourier Transformation (IFFT) process. Through a Cyclic Prefix (CP) adding process, a CP is added to the time domain signal after the IDFT or IFFT process as a guard interval. The intersymbol interference may be reduced greatly or even eliminated, and the orthogonality between channels may be guaranteed, so that inter-channel interference may be reduced greatly.
At present, the Multimedia Broadcast/Multicast Service (MBMS) based on the OFDM multicarrier technology is one of the important services of Long-Time Evolution (LTE). The MBMS service refers to a service in which the network side broadcasts or multicasts the same multimedia data to a plurality of receivers in the network simultaneously. At present, the multimedia data mainly includes stream services and background services.
As described above, in order to reduce the intersymbol interference caused by a multipath delay, a CP is usually added to a time domain signal after the IDFT or IFFT process. The longer the CP added is, the stronger the ability to resist the intersymbol interference caused by multipath delay will be. However, a too long CP may also result in a low transmission efficiency. Therefore, in different OFDM systems, the length of the CP added may be configured as different values according to different applications.
In the LTE, the CP includes a short CP and a long CP. The time length of the short CP is about 4.7 μs, i.e., TCP≈4.7 μs, and is mainly used in a non-broadcast service (Unicast). The time length of the long CP is about 16.7 μs, i.e., TCP≈16.7 μs, and is mainly used in MBMS or cell with a larger diameter. For cells with smaller diameters, or when the system sends a Unicast service, the short CP is employed. When the system sends an MBMS service or when the cell diameter is larger, the long CP is employed.
Usually, a system sends the Unicast service and the MBMS service after a Time Division Multiplexing (TDM) process is performed; in other words, some sub-frames are used for delivering the MBMS service and some sub-frames are used for delivering the Unicast service.
FIG. 2 is a schematic diagram showing the state of the TDM process for the Unicast service and MBMS service in the prior art. In FIG. 2, a short CP is used in Sub-frame 0, Sub-frame 2, Sub-frame 3 and Sub-frame 6 to deliver Unicast service. Base stations between cells schedule and send Unicast service data independently. A long CP is used in Sub-frame 1, Sub-frame 4 and Sub-frame 5 to deliver MBMS service, and each cell sends the same MBMS service data. A User Equipment (UE) demodulates the MBMS service data sent by the system according to corresponding control information. If the UE lies in the cell edge, a plurality of MBMS service signals received from a plurality of cells may be merged through a combining mode, so that the signal-to-noise ratio and the coverage percentage of the cell edge may be improved.
At present, the mode for performing the TDM for the MBMS service and the Unicast service includes a scheduling mode and a designating mode.
The scheduling mode is performed according to the Quality of Service (QoS) of the Unicast service data and MBMS service data. When the QoS requirement for the MBMS service data is stricter than that for the Unicast service data, the MBMS service data will be scheduled firstly; otherwise, the Unicast service data will be scheduled first. Because the MBMS service needs to be sent between a plurality of adjacent cells simultaneously, the QoS requirement for the MBMS service between the cells may be the same. However, the QoS requirement for the Unicast service in each cell may hardly be the same. Therefore, during the TDM process in the scheduling mode a frequent switching between the MBMS service sub-frame and the Unicast service sub-frame will be caused, and the system signaling overhead will be increased greatly.
The designating mode refers to that, only the QoS requirement for the MBMS service will be considered in the two services; in other words, the system will designate the sub-frames for delivering the MBMS service data according to the delay requirement and rate requirement of the MBMS service. As shown in FIG. 2, the system may designate Sub-frame 1, Sub-frame 4 and Sub-frame 5 to deliver the MBMS service data according to the QoS requirement for the MBMS service. Therefore, it can be seen that the delivery priority of the Unicast service will be neglected in the designating mode. As a result, the delay of the Unicast service is increased and the delay is intolerable for the Unicast service with a strict delay requirement.